assault vs set upon

assault is a noun but set upon is not a noun.

Word	Noun	Adjective	Verb	Adverb
assault	Yes	No	Yes	No
set upon	No	No	Yes	No

As verbs, set upon is a hyponym of assault; that is, set upon is a word with a more specific, narrower meaning than assault:

assault (noun)	set upon (noun)
close fighting during the culmination of a military attack
a threatened or attempted physical attack by someone who appears to be able to cause bodily harm if not stopped
the crime of forcing a person to submit to sexual intercourse against his or her will

assault (verb)	set upon (verb)
attack in speech or writing	assail or attack on all sides:
attack someone physically or emotionally
force (someone) to have sex against their will